1. Field of the Invention
The present invention relates to a highly integrated read-only memory (ROM) which is at a low cost, and a method of fabricating the same.
2. Background of the Invention
In a mask ROM which is a nonvolatile memory, data are written in response to masking patterns in a stage of fabrication and a basic structure of each memory cell is formed by a 1-bit single transistor, whereby an occupied area per bit is small as compared with other reloadable memories. Thus, the mask ROM is suitable for mass storage and mass production. Through such characteristics, short delivery is strongly required in a mask ROM applied field of office automation products and games handling large quantities of fixed data in relation to implementation of mass storage, increase in speed and production cycles for attaining high function and high performance of products, and development has been made in order to cope with such requirement.
At present, 8-megabit memories are now in full-scale mass production, followed by 16-megabit ones. Further, 32-megabit memories are now reaching the end of development. In consideration of memory cell sizes, operating speeds and TAT (turn around time), memory cells of mask ROMS having basic structures of 1-bit single transistors are classified into two types including those of a NOR type flat memory cell system (first prior art) shown in FIG. 40 and a NAND type system (second prior art) shown in FIG. 43 in currently available 2-megabit mass storage ROMs or those of larger capacity.